Format a Number, Exactly Two in Length?

Question

I have an integer that is less then 100 and is printed to an HTML page with JavaScript. How do I format the integer so that it is exactly two digits long? For example:

Answer 1

Just use the following short function to get the result you need:

function pad2(number) {
    return (number < 10 ? '0' : '') + number
}

Answer 2

Improved version of previous answer:

var result = [...Array(12)].map((_, i) => zeroFill(i + 1, 2));

function zeroFill(num, size) {
  let s = num + '';
  while (s.length < size) s = `0${s}`;
  return s;
}
console.log(result)

Answer 3

A direct way to pad a number to the left in Javascript is to calculate the number of digits by log base 10. For example:

function padLeft(positiveInteger, totalDigits) {
  var padding = "00000000000000";
  var rounding = 1.000000000001;
  var currentDigits = positiveInteger > 0 ? 1 + Math.floor(rounding * (Math.log(positiveInteger) / Math.LN10)) : 1;
  return (padding + positiveInteger).substr(padding.length - (totalDigits - currentDigits));
}

The rounding factor fixes the problem that there is no way to get an exact log of powers of 10, for example Math.log(1000) / Math.LN10 == 2.9999999999999996 Of course one should add validation of the parameters.

Answer 4

function padLeft(a, b) {
    var l = (a + '').length;
    if (l >= b) {
        return a + '';
    } else {
        var arr = [];
        for (var i = 0; i < b - l ;i++) {
            arr.push('0');
        }
        arr.push(a);
        return arr.join('');
    }
}

Answer 5

function pad(d) {
    return (d < 10) ? '0' + d.toString() : d.toString();
}

pad(1);  // 01
pad(9);  // 09
pad(10); // 10

Answer 6

String("0" + x).slice(-2);

where x is your number.